Water-Immersible Micromachined Pb(Zr, Ti)O3 Thin Film Actuators

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We demonstrate a water-immersible thin film lead zirconate titanate, Pb(Zr, Ti)O3, [PZT] actuator, without special passivation layer, towards in-vivo or in-vitro scanning probe microscope (SPM) measurements of living cells in water or biological fluids. In order to be water-immersible, the electrodes need to be electrically insulated and the piezoelectric layer needs to be protected against direct water contact. This paper describes our design solution with a simple fabrication process for a water-immersible piezoelectric device, which separates the bottom electrode from the top electrode by having a narrow ditch covered with PZT film. The PZT film is then encapsulated with the top metal electrode without insulation layer. In this structure, the PZT is sandwiched between the top and bottom metal electrodes to prevent water permeation. The device is fabricated using lift-off processing for the bottom and top electrodes, sol-gel spinning for the PZT thin film and wet etching for the PZT patterning. The piezoelectric constant, d31, is about −100 pC/N. The dielectric polarization and fatigue properties of the devices were measured in air and water. The spontaneous polarization, remnant polarization, coercive field and dielectric constant are 54 μC/cm2, 15 μC/cm2, 60 kV/cm and 1200, respectively. The polarization property of the device was unchanged in either air or water up to 1 × 109 continuous cycles.

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